Conventionally, in a recliner mechanism adjusting an inclination angle of a backrest seat, one side case provided with an engagement gear and the other side case provided with a slide groove guiding movement of a sliding rock member engaged with and released from the engagement gear are mounted integrally so that the one side case and the other side case are rotated freely by an attachment member, and this configuration is well-known (Patent Literature 1).
In the above well-known example, a tubular attachment member is attached by a so-called caulking processing, in which the tubular attachment member is covered on the outer circumferences of the one side case and the other side case and pressure is applied from a cross direction to a shaft center direction of the one side case and the other side case to deform the attachment member, so that the one side case and the other side case are freely rotated.